The present invention relates to a cross-connection network for use in digital transmission and in particular, to the cross-connection network for interchanging transmission paths of time division multiplexed signals to one another in a station.
The cross-connection network is for use in initial route setting of transmission paths and change of routes which are necessary on an increase of transmission paths, change of services, and occurrence of a fault.
With an extension of available field of digital communication, recent requirements are directed to a reduction of size in a device, a decrease of a space for laying cables, saving labor for cross connection, and a variation of switchable hieratchy levels, in such a cross-connection network.
A conventional cross-connection network of the type described uses a distribution frame comprising switch groups switching mutual connection or cross connection of a plurality of signal lines (for example, coaxial cables) from one to another. The switches are manually operated.
Such a digital signal transmitted on the transmission paths is classified into two types one of which is of a synchronous type and the other being of an asynchronous type. For the digital signal of the asynchronous type, a space division switch alone is used to carry out cross connection of the signal lines as the switch groups in the distribution frame because no consideration is made about application of a time division switch so as to interchange time slots from one to another.
Such use of a space division switch in the cross-connection network results in difficulties of a reduction of devices in size, saving the space for laying the transmission cables, and a change of switching units. Therefore, it is impossible to completely respond to the above-mentioned recent requirements.
More specifically, a restriction is imposed on reducing the space division switch in size, although the time division switch can readily be small sized by integrating circuits.
In addition, it is necessary to switch connections from one to another at every unit formed by a lower order group by demultiplexing a higher order group into a plurality of the lower order groups in order to cope with a wide variety of switching units. For this purpose, the conventional network comprising the space division switch should comprise a demultiplexer for demultiplexing the digital signals of the higher order group into lower order groups which are sent to the distribution frame. The network further comprises a multiplexer for multiplexing the lower order groups into a higher order group which is sent out from the network. Thus, the cross-connection network inevitably includes the multiplexer and the demultiplexer in addition to the distribution frame. In order to transmit the demultiplexed digital signals of the lower order group, signal lines are inevitably increased in number. This makes a reduction of the device and the collecting space impossible.